[Do you mean to say that St. Peter is not at least in some sense the Rock of Matthew 16:18?
For an Orthodox Catholic interpretation of the 'ROCK' you can access the following website -http://aggreen.net/peter/st_peter.html
What did some of the pre-schism early church fathers have to say about 'Peter and the ROCK' -
Cyprian, unwilling to grant even a simple primacy to the Bishop of Rome, considers that "the whole body of bishops is addressed
in Peter." St. Cyprian rightly concludes that the "Rock is the unity of faith, not the person of Peter." (De Catholicae Ecclesiae Unitate,
"I believe that by the Rock you must understand the unshaken faith of the apostles." (St. Hilary, 2nd Book on the Trinity)
Of all the Fathers who interpret these passages in the Gospels (Matthew 16:18, et. al.) NOT A SINGLE ONE OF THEM applies these
passages to the Roman bishops as Peter's successor. How many Fathers had busied themselves with these texts, yet not one of them whose
commentaries we possess, Origen, Chrysostom, Hilary, Augustine, Theodoric... has dropped the faintest hint that the primacy of Peter is the consequence of the commission and
promise to Peter. Not one of them has explained the Rock or foundation on which Christ will build His Church as the office given to Peter to be transmitted to his successors, but
they understood by it either Christ Himself, or Peter's confession of faith in Christ, often both together. Or else they thought Peter was the foundation equally with the other apostles,
the twelve being together the foundation stones of the Church." (Ignaz von Dollinger, The Papacy and the Council, p. 91)
"This one (Peter) is called a rock in order that on his FAITH (Rock) he may receive the foundations of the Church." - St. Gregory Nazianzen,
"The Rock on which Christ will build His Church means the faith of confession." - St. John Chrysostom, 53rd Homily on St. Matthew
"The Rock (petra) is the blessed and only rock of the faith confessed by the mouth of Peter. It is on this Rock of the confession of faith that
the Church is built." - St. Hilary of Poitiers, 2nd book on the Trinity
Hilary wrote the first lengthy study of the doctrine of the Church in Latin. Proclaimed a "Doctor of the Church" by the Roman See in 1851, he is called the Athanasius of the
Cyril of Alexandria
Upon St. John, Book JJ, Chap. XII
'"The word "Rock" has only a denominative value-it signifies nothing but the steadfast and firm faith of the apostles."
In his Letter to Nestorius, St. Cyril says:
"Peter and John were equal in dignity and honor. Christ is the foundation of all -the unshakeable Rock upon which we are all built as a
"Christ is the Rock Who granted to His apostles that they should be called rocks. God has founded His Church on this Rock, and it is from
this Rock that Peter has been named." - St. Jerome, 6th book on Matthew
"Faith is the foundation of the Church, for it was not of the person but the faith of St. Peter of which it was said, 'the gates of hell shall not
prevail'; certainly it is the confession of faith which has vanquished the powers of hell."
"Jesus Christ is the Rock. He did not deny the grace of His name... to Peter because he borrowed from the Rock the constancy and solidity of
his faith- thy Rock is thy faith, and faith is the foundation of the Church. If thou art a Rock, thou shalt be in the Church, for the Church is
built upon the Rock... (the profession of faith in Christ Jesus)." - St. Ambrose: The Incarnation
(Note: St. Ambrose often spoke disparagingly of the Bishop of Rome as usurping the legitimate rights of other bishops in the Church. Cf. On the Incarnation, On St. Luke, and
On the 69th Psalm.)
St. Augustine, one of the most renowned theologians of the Western Church, claimed by the Roman See as "Father and Doctor", says:
"In one place I said... that the Church had been built on Peter as the Rock... but in fact it was not said to Peter, "Thou art the Rock," but rather "Thou art Peter." The Rock was
Jesus Christ, Peter having confessed Him as all the Church confesses Him, He was then called Peter, "the Rock"... (ed, for his faith) ...Between these two sentiments let the reader
choose the most probable." (St. Augustine, Retractions - 13th Sermon; Contra Julianum 1:13)
St. Augustine also adds: "Peter had not a primacy over the apostles, but among the apostles, and Christ said to them "I will build upon Myself, I will not be built upon thee."
To Augustine, this made Peter somewhat less than an infallible teacher, without his fellow bishops and all the faithful by his side. It is this statement by Augustine which Pope
Hadrian VI (1522-25) had in mind when he declared:
"A Pope may err alone, not only in his personal, but official capacity."
In still another letter Augustine quotes Cyprian, with whom he is in full agreement:
"For neither did Peter whom the Lord chose... when Paul afterwards disputed with him... claim or assume anything and arrogantly to himself, so as to say that he held a primacy
and should rather be obeyed by newcomers..."
Finally, Augustine concludes, near the end of his earthly life, with these words on the "Rock of the Church":
"Christ said to Peter... I will build thee upon Myself, I will not be built upon thee. Those who wished to be built among men said, 'I am of Paul, I am of Apollos, I am of
Cephas' - however, those who did not wish to be built upon Peter but upon the Rock say, I am of Jesus Christ." (Retractions, 13th Sermon)